A suppression list is a list of email addresses that must not receive marketing email from you, whatever list or segment they appear in. It typically includes people who unsubscribed, addresses that hard-bounced, people who reported spam, addresses removed at the person’s request and any you have blocked manually, such as competitors or role addresses you don’t want to mail.
Its value lies in being applied everywhere. If someone unsubscribes from your newsletter and is then re-added through a spreadsheet import, a form on another site or an integration, the suppression list should still stop them receiving marketing. Without it, people who asked to leave keep getting emails, which causes complaints and, under consent laws, can be a breach.
Suppression is different from deletion. If you delete an unsubscribed contact entirely, you lose the record that they asked not to be emailed, and the next import may add them back as if they were new. Keeping just the address on a suppression list respects their choice while holding very little personal data. Some platforms also support suppressing whole domains, useful for blocking a company that has asked not to be contacted.
When you move between email platforms, export your suppression list along with your contacts and import it into the new platform before your first send. This is one of the most commonly forgotten migration steps, and forgetting it means emailing every past unsubscriber again on day one.
A Bengaluru startup imports 5,000 contacts from its CRM. 230 of them had unsubscribed from its newsletter earlier and 40 had hard-bounced. Because their addresses are on the suppression list, they are skipped automatically, and the campaign goes only to the remaining contacts.
MailNesto keeps a suppression list covering unsubscribes, bounces, complaints, erasure requests and manual entries, can suppress whole domains, and applies it to every send.